The animal family Sepiidae is one commonly known for its high intelligence and creative strategies to go about survival. However, one look at the Life History of these species and we gain a considerable amount of insight into their scientific plans and how these plans succeed and fail. In order to avoid the spotlight being shown on one species in particular, reference to the species will be the term “sepiids.”
Starting at the beginning, when sepiids are born they are identifiable as benthic species. The young will look like the adults and full grown species when they hatch. The large eggs that are stored in the oviducts of the female are coated with oviductal secretion as well as other forms of secretion during the spawning. After the eggs have been deposited, embryonic development is highly dependent on temperature and will fail to hatch correctly if the environment is too hot or too cold. Whilst eggs are laid in the Spring, the spawning season is usually during the Summer ranging from July to August during the warmer temperatures. During the rut, or the time when males clash for the right to breed, male sepiids will range in size from 6 inches to 10 inches ensuring the bigger bull males will ensure victory in most of their fights. Typical species like Sepiida will grow rapidly but the largest species in the family Sepia apama, can reach up to 20 inches and weigh up to 23lbs in mass.
Growth of young sepiids is considered to be rather quick as the conversion rate is 30-40% (Pascual, 1978). Newborns are typically 0.75 inches long, reaching a full inch about two months after being born. Approximately 200 to 250 eggs can be laid in a single clutch, although it is often difficult to analyze the specific number as females typically lay their clutches near those of other females. This can be effective such as the sepiids are an R species, the parents opt in having quantity rather than quality. We see this trade-off especially in mother sepiids who have just laid they clutch. Shortly after the female lays her eggs, she dies. A process called Senescence is common in cephalopods and essentially rots the still living individual in place, ensuring that when the young finally hatch, the mother and father are no longer living and won’t be able to respectively take care of the young. This cost of reproduction might sound like a losing situation but with the number of eggs an individual can lay/fertilize, along with the shortened life span of an average 2 years, the sepiids cannot afford to stick around and nurture their young.
Additionally, these shallow water sepiid populations have evolved eggs that allow the offspring to survive with minimal investment from the parent. These eggs contain a yolk equipped with enough nutrients to sustain the embryo for several days until it is ready to find its own food(Young 2019). The
Sepiids travel to shallow coastal waters in the spring and summer months to find mates and reproduce. Many of the coastal regions where reproduction takes place are highly variable and subject to intense coastal storms with shorelines that sepiids are commonly found in experiencing wind gusts up to eighty miles per hour (BBC 2014). These dangerous reproductive sites’ high mortality rates helps explain why we see sepiids display r species characteristics producing high amounts of offspring with minimal investments they are to ensure the survival of their lineage.
These populations that tend to migrate to shallow, shore water for reproduction reach age of sexual maturity quickly are therefore smaller in size than some of the sepiid populations that reside in deep-water environments where the conditions are more stable and the mortality rates are lower (Britannica 2020). As a result, these deep water populations tend to produce less offspring and invest more resources into the fewer numbers that they do reproduce. Additionally, these species have a larger RRV value early in life, which then declines as they reach the age of sexual maturity, meaning the population invests more of their resources initially in growth, and then into reproduction later on. Here, we see the tradeoff of quality of offspring being selected for over quantity as the stable, unchanging deep sea environment affords them the opportunity to delay reproduction until later in life, and as a result they are larger at the age of maturity(Bolstad 2019). These deep water populations of sepiids reflect more of the concept of the K selected species having a later age of reproduction with lower mortality rates. The shore-occupying populations are more in line with r selected species having a short lifespan and a quick maturation process so that they can reproduce before they die as they live in a higher-mortality environment.
Life History Theory
Cuttlefish egg adapted with a large yolk
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